(1) Field of the Invention
The present invention relates to a reconfigurable optical device for Wavelength-Division Multiplexing networks.
The increasingly vast diffusion of the Internet and consequent demand for an increasingly wide band in optical communications has led to the by now uncontested success of the Wavelength-Division Multiplexing (WDM) transmission system.
The advantage of this configuration is that, by modulating several carriers independently at different wavelengths, it is possible to make optimum use of the extremely wide band offered by optical fibres with technologies already available on the market.
Nonetheless, the bottleneck of these transmission systems currently lies in the specifications of the signal processing and routing devices, which are implemented with opto-electronic technologies, which limit the band that can actually be used in optical communications.
Scientific research aimed at producing these devices in a completely optical manner is thus understandably extremely active, both on the industrial and the scientific-university sides.
(2) Description of Related Art
One of the devices that arouses the most interest is undoubtedly the one that performs the functions of “add/drop”; as already mentioned, the WDM signal is formed of several carriers, modulated independently from one another and each at a different wavelength.
In dynamic management of a telecommunications network, it is frequently necessary to drop only one of the channels of the WDM signal (“drop” function), for example to route it to another communication line, or to add a channel to a WDM signal at a wavelength that has remained empty.
The devices proposed to date to produce these functions are based on linear optical effects and can be divided into two categories: the first uses the “arrayed waveguide gratings” with the addition of thermo-optical switches or phase shifters, while the second comprises all those configurations in which two waveguides are coupled by means of an extremely narrow band-pass filter.
These band-pass filters can be produced by a Bragg grating written in the coupling zone of two fibres, between two vertically coupled semiconductor waveguides, in a Mach-Zehnder interferometer or, lastly, by fitting micro-ring resonators at the cross-points of two waveguides.
In any case, the problems of these configurations are considerable and essentially lie in the high losses of the first type of devices and the lack of propensity, if not impossibility, to be reconfigured in devices of the second type.
Finally, when the number of channels contained in the WDM signal increases, there is an increase in the complexity and number of elements involved in architectures based on previous devices, with evident disadvantages as regards cost and technology.
The object of the present invention is thus to produce a reconfigurable optical device for wavelength-division multiplexing networks which obviates the problems mentioned above, or to indicate a reconfigurable optical device that avoids the problem of filtering with an extremely narrow band, moving the function from the coupler to the non-linear process for generating a sum frequency in a first waveguide.
Another object of the present invention is to indicate a reconfigurable optical device for wavelength-division multiplexing networks that allows only one channel of those forming the WDM signal to be selectively dropped without modifying the remaining channels.
A further object of the present invention is to produce a reconfigurable optical device for wavelength-division multiplexing networks that allows any channel forming the WDM signal to be dropped and, at the same time, is sufficiently simple to use, easy to rescale and transparent to the number of channels of the WDM signal, compared with known structures.
These objects can be attained with a reconfigurable optical device for wavelength-division multiplexing networks according to claim 1, which is referred to for brevity.